(a) Field of the Invention
This disclosure relates to a polymer ion exchange membrane having self-hydration capability under low humidity conditions, and a method of preparing the same.
(b) Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through the electrochemical redox reaction of an oxidant and hydrogen included in a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like.
Such a fuel cell is a clean energy source that can replace fossil fuels. It includes a stack composed of unit cells, and has an advantage of producing various ranges of power. Since it has a four to ten times higher energy density than a small lithium cell, it has been high-lighted as a small portable power source.
Typical examples of a fuel cell are a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell which uses methanol as a fuel is called a direct methanol fuel cell (DMFC).
In a fuel cell, the stack that actually generates electricity includes several to scores of unit cells stacked in multiple layers. Each unit cell is made up of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (referred to as a fuel electrode or an oxidation electrode), a cathode (referred to as an air electrode or a reduction electrode), and a polymer electrolyte between the anode and the cathode, and the polymer electrolyte membrane is attached to the anode and the cathode through a proton ion conductive binder.
Electricity in a fuel cell is generated as follows: a fuel is supplied to an anode and adsorbed in catalysts of the anode, and then oxidized to produce protons and electrons. The electrons are transferred into the cathode, an oxidizing electrode, via an electric conductive external circuit, while the protons are transferred into the polymer electrolyte membrane through a proton conductive binder by passing through the polymer electrolyte membrane including a proton conductive polymer, and then through a proton conductive binder, and reach the cathode. In addition, an oxidant is supplied to the cathode. Then, the oxidant, protons, and electrons are reacted on catalysts of the cathode to produce electricity along with water.
It is important for a fuel cell stack system used for vehicle transportation and the like to maintain the membrane-electrode assembly in a hydrated state to secure sufficient ion conductivity, and thus requires additional fuel humidifying and cooling apparatuses.